Evaluation of scattered-light signals in an optical hazard alarm and output both of a weighted smoke density signal and also of a weighted dust/steam density signal
View Patent ↗A method evaluates two scattered-light signals in a hazard alarm operating in accordance with the scattered light principle. The particles to be detected are irradiated with light in a first wavelength range and with light in a second wavelength range. The light scattered by the particles is converted into a first and second non-normalized scattered light signal. The two scattered light signals are normalized in relation to one another such that their amplitude curve approximately coincides for larger particles such as dust and steam. The two normalized scattered light signals are transformed into a polar angle and a distance as polar coordinates of a polar coordinate system. Finally a respective smoke density signal and a respective dust/steam density signal is formed from a current distance value, wherein for this purpose the respective current distance values, depending on a current polar angle value, are weighted in opposition to one another.
1. A method for evaluating two scattered light signals in a hazard alarm operating in accordance with a scattered light principle, the method comprising:
irradiating particles to be detected with a first light in a first wavelength range and with a second light in a second wavelength range;
converting light scattered by the particles into respective first and second non-normalized signals correspondingly from said first and second lights, respectively;
normalizing the first and second non-normalized signals to one another and producing two normalized scattered light signals having amplitude curves that approximately coincide for dust- and steam-sized particles;
transforming the two normalized scattered light signals as a ratio into a polar angle and a polar distance as polar coordinates of a polar coordinate system;
forming a weighted smoke density signal and a weighted dust/steam density signal by weighting the polar distance depending on the polar angle, the polar distance being weighted oppositely in forming the weighted smoke density signal and the weighted dust/steam density signal; and
outputting the weighted smoke density signal and the weighted dust/steam density signal for further evaluation of the hazard alarm.
2. The method as claimed in claim 1 , wherein
the weighted smoke density signal is compared in a smoke comparison with a smoke signal threshold and a fire alarm stage is signaled based on the smoke comparison, and/or
the weighted dust/steam density signal is compared in a dust/steam comparison with a dust/steam signal threshold and a dust/steam warning stage is signaled based on the dust/steam comparison.
3. The method as claimed in claim 1 , wherein
if the polar angle is formed from as a quotient between first and second normalized scattered light signals, then:
the polar distance is weighted degressively during formation of the weighted smoke density signal for increasing polar angle values, and
the polar distance value is weighted progressively during formation of the weighted dust/steam density signal for increasing polar angle values, and
if the polar angle is formed from as a quotient between second and first normalized scattered light signals, then:
the polar distance is weighted progressively during formation of the weighted smoke density signal for increasing polar angle values, and
the polar distance is weighted degressively during formation of the weighted dust/steam signal for increasing polar angle values.
4. The method as claimed in claim 1 , wherein
the first light is infrared light and the first wavelength range is between 600 and 1000 nm, and
the second light is blue light and the second wavelength range is between 450 and 500 nm.
5. The method as claimed in claim 1 , wherein
the first light is infrared light and the first wavelength range is 940 nm±20 nm, and
the second light is blue light and the second wavelength range is 470 nm±20 nm.
6. The method as claimed in claim 1 , wherein the first and second non-normalized signals are normalized to amplitude curves that approximately coincide for particles having a particle size 0.5 and 1.1 μm.
7. An optical hazard alarm operating in accordance with a scattered light principle, comprising:
a detection device comprising:
at least one light source to irradiate particles to be detected with a first light in a first wavelength range and with a second light in a second wavelength range; and
an optical receiver to convert light scattered by the particles into respective first and second non-normalized signals correspondingly from said first and second lights, respectively; and
an electronic evaluation unit comprising:
a normalization unit to normalize the first and second non-normalized signals to one another and produce two normalized scattered light signals having amplitude curves that approximately coincide for dust- and steam-sized particles;
a processor to transform the two normalized scattered light signals as a ratio into a polar angle and a polar distance as polar coordinates of a polar coordinate system; and
a signal formation unit to form a weighted smoke density signal and a weighted dust/steam density signal by weighting the polar distance depending on the polar angle, the polar distance being weighted oppositely in forming the weighted smoke density signal and the weighted dust/steam density signal, the weighted smoke density signal and the weighted dust/steam density signal being output for further evaluation of the hazard alarm.
8. An optical hazard alarm as claimed in claim 7 , wherein
if the polar angle is formed from as a quotient between first and second normalized scattered light signals, then:
the polar distance is weighted degressively during formation of the weighted smoke density signal for increasing polar angle values, and
the polar distance value is weighted progressively during formation of the weighted dust/steam density signal for increasing polar angle values, and
if the polar angle is formed from as a quotient between second and first normalized scattered light signals, then:
the polar distance is weighted progressively during formation of the weighted smoke density signal for increasing polar angle values, and
the polar distance is weighted degressively during formation of the weighted dust/steam signal for increasing polar angle values.
9. The optical hazard alarm as claimed in claim 7 , wherein
the first light is infrared light and the first wavelength range is between 600 and 1000 nm, and
the second light is blue light and the second wavelength range is between 450 and 500 nm.
10. The optical hazard alarm as claimed in claim 7 , wherein
the first light is infrared light and the first wavelength range is 940 nm±20 nm, and
the second light is blue light and the second wavelength range is 470 nm±20 nm.
11. The optical hazard alarm as claimed in claim 7 , wherein the first and second non-normalized signals are normalized to amplitude curves that approximately coincide for particles having a particle size 0.5 and 1.1 μm.
12. The optical hazard alarm as claimed in claim 7 , wherein the electronic evaluation unit has:
a comparison unit to compare the weighted smoke density signal with a smoke signal threshold; and
a signaling unit to signal a smoke alarm stage based on the comparison.
13. The optical hazard alarm as claimed in claim 7 , wherein the electronic evaluation unit has:
a comparison unit to compare the weighted dust/steam density signal with a dust/steam signal threshold; and
a signaling unit to signal a dust/steam warning stage based on the comparison.